1. Field of the Invention
The present invention relates to a recovery method of highly pure alkyl lactate and lactic acid.
2. Description of the Related Art
There has been an increased amount of usage in lactic acid in recent years, which is a base material for biodegradable polymer, polylactic acid. Lactic acid is also widely used as the base material for chemistry, cosmetics and food. Lactic acid is generally produced by fermentation because production by fermentation is more environmentally friendly and economical than production by chemical synthesis.
Also, there has been an increasing demand for ethyl lactate, which can be used as food additives, spices, as well as an environmentally friendly solvent that can substitute the toxic halogen solvents because they are less volatile, have less odor, stable at temperatures over 150° C., have high solvency and are biodegradable. In addition, lactic acid can be used as a base material for lactide, which is the monomer of polylactic acid (PLA) that is becoming popular as a biodegradable polymer.
When producing lactic acid by fermentation, lactic acid is generally produced by fermentation process of carbohydrate such as glucose with anaerobic bacteria. To increase the fermentation productivity, lactic acid fermentation process is usually performed at pH range of 5 to 6. Basic compounds such as ammonia or calcium carbonate are added as pH regulators. Therefore, the lactic acid formed by above method will exist in the form of ammonium lactate or calcium lactate. Since the solubility of calcium lactate in water is less than 80 g/liter, the calcium lactate precipitate in the fermentation solution will inhibit the fermentation, limiting the final concentration of lactic acid to below 10%. Therefore, it is advantageous to use ammonium lactate form in the fermentation process in terms of productivity, since the fermentation concentration can be increased up to 20% due to its higher solubility in water.
Although the fermentation productivity of calcium lactate is very low, the lactic acid can be separated easily from the fermentation broth of calcium lactate by treating it with sulfuric acid followed by separation of calcium sulfate precipitate.
Therefore, calcium lactate fermentation method has been widely used for commercial lactic acid fermentation and purification process, despite the problem of calcium sulfate waste overproduction, known as gypsum.
Although the fermentation productivity of ammonium lactate is very high, its recovery process into lactic acid is quite complicated.
For example, U.S. Pat. No. 6,291,708 discloses a method for decomposing ammonium lactate liquid solution using high pressure, and U.S. Pat. No. 5,723,639 discloses a method for manufacturing lactic acid using electrodialysis method and membrane techniques. However, there are several problems; the high investment cost for equipments for dissociating at high pressure and membrane, the slow reaction rate, and finally, the low final concentration of lactic acid produced.
In addition, Korean Patent Application Laid-open Publication No. 2003-0030575 discloses a Method for increasing the production of lactic acid from food waste using enzyme hydrolysis and fermentation method,
Korean Patent Application Laid-open Publication No. 2003-0008187 discloses a fermentation process using the fermentation medium containing lignocelluloses as the carbon source and inoculating the media with lactic acid-fermenting microorganism,
Korean Patent Application Laid-open Publication No. 2003-0032982 discloses a method for producing lactic acid using natural culture media consisting of liquified/saccharified wheat bran without adding any other chemical materials,
Korean Patent Application Laid-open Publication No. 10-2005-0097719 disclosed a method for producing lactic acid by producing saccharified solution from fibrous biomass at optimal temperature of the saccharification enzymes, and then adding the lactic acid-forming microorganism into the fermentor filled with the saccharified liquid,
Korean Patent Application Laid-open Publication No. 10-2005-0010986 disclosed a method of producing lactic acid by using tapioca starch saccharified solution as the source material and culturing the lactic acid-fermenting microorganism for lactic acid biosynthesis,
Korean Patent Application Laid-open Publication No. 10-2008-0065610 disclosed a microorganism with lactic acid-fermenting activity with part or all of its protein with 4-hydroxybenzoic acid polyprenyl transferase activity, or 2-octaprenylphenol 2-octapreny-6-methoxyphenol; flavin reductase activity are reduced or lost, in particular, a microorganism with all or part of its chromosomal DNA coding for proteins with 4-hydroxybenzoic acid polyprenyl transferase activity, or 2-octaprenylphenol 2-octapreny-6-methoxyphenol; flavin reductase activity is missing, and the method of producing lactic acid using the microorganism thereof.
However, the traditional techniques for producing lactic acid by fermentation fail to describe a recovery method of highly pure lactic acid.
In addition, lactic acid is produced by esterification reaction of ammonium lactate fermentation liquid with alcohol to form alkyl lactate, and then hydrolyzed to lactic acid. The esterification reaction between ammonium lactate and alcohol has low efficiency because of the catalyst inhibition by ammonium ion. Therefore, a high temperature/pressure condition is required to improve the efficiency, which may cause high costs. The production of lactic acid oligomer and lactamide as the reaction by-product may also cause a problem.
In addition, there is a method of treating ammonium lactate with sulfuric acid to convert into ammonium sulfate and lactic acid, but the solubility of ammonium sulfate is 74.4 g in 100 ml of water at 20° C., which is very high, therefore it is impossible to recover lactic acid from ammonium lactate using ammonium sulfate precipitation and filtration method.
In addition to the above recovery methods, there are other methods such as ion exchange, affinity, extraction and distillation for recovering lactic acid. Lactic acid has a very high affinity to water and alcohol, and is a nonvolatile (or very low volatile) material; so it is difficult to isolate it using distillation method which is widely used in the industry. Distillation under reduced pressure may be used, but a high vacuum pressure is required, which causes a problem of investment in extra plant and equipments.
Therefore, a technology for recovering lactic acid from the fermentation broth of ammonium lactate that is economical and gives higher yield than the conventional method is required.
Also, the lactic acid ester, alkyl lactate is a biodegradable ethyl lactate which is gaining importance for its wide usage as an environmentally friendly solvent. Similar with lactic acid, there is a high demand for economical techniques of recovering and purifying highly pure alkyl lactate from lactic acid fermentation liquid.
Therefore, the present inventors completed a recovery method of highly pure alkyl lactate by adding alcohol and sulfuric acid to the source liquid comprising lactic acid and ammonium sulfate that is cost effective than the conventional method; and also completed a recovery method of highly pure lactic acid by hydrolyzing pure alkyl lactate, which is cost effective than the conventional method.